This invention relates, in general, to Doppler radar, and more specifically, to proximity sensors.
Conventional proximity sensors, such as are used in fuzes for projectiles and missiles, use a system for locating and tracking a target called phase locked loop. This system continuously transmits and receives electromagnetic waves which operate to supply a Doppler frequency to the receiver. This Doppler frequency allows the fuze system to determine when the target is within a close proximity to the projectile. When the target is in close proximity to the projectile, the fuze is detonated and the projectile explodes.
When the target is first located by the sensor, the sensor will receive only a single Doppler profile. However, if the target has more than one surface reflecting electromagnetic waves back to the receiver, as the target gets closer to the projectile, several Doppler profiles become apparent from the various surfaces, each target surface represented by a different Doppler frequency whose magnitude depends on the surface's distance from the receiver. The multiple profiles give the sensor several targets rather than one target, and cause the fuze to be detonated on a profile which follows in time to the ideal detonating time and profile since the sensor cannot distinguish between the various Doppler frequencies.